1. Field of the Invention
The present invention pertains to marine propulsion systems generally, and more specifically to marine propulsion systems utilizing an elongated propeller drive shaft having a housing surrounding the propeller shaft.
2. Description of the Related Art
Modern marine vehicles are most commonly powered by an internal combustion engine mounted within the boat or above the water line adjacent the boat. The mechanical power generated by the engine is transferred through a drive shaft to a water propulsion device such as a propeller. These marine vehicles provide a mode of transportation for traversing bodies of water that may be relatively large and open, such as the larger lakes, rivers and oceans, or relatively smaller, such as streams or creeks, swamps, glades, savannahs and the like.
For boating in open waterways such as lakes, rivers or the oceans, the propeller shaft is typically relatively short, and may extend from the motor and away from the boat hull only a few inches or feet. The spacing between propeller and hull in this type of boat is substantially smaller than the overall length of the boat. This short propeller shaft also dictates that the propeller is placed fairly deep into the water, to allow water to circulate past the boat hull and reach the propeller, and to avoid interference between propeller and boat hull during turns and the like. In open waters, where few if any obstacles exist, this arrangement has proven to be very effective and is represented by standard inboard and outboard marine propulsion systems.
Unfortunately, when traversing smaller or shallower bodies of water, such as swamps, creeks and streams, the rounded boat hulls and deep propeller arrangements used in open waterways are no longer effective or useful. The hull runs deeper than some sections of these smaller waterways, or obstacles present therein, and the propeller readily becomes tangled in vegetative matter, or, worse, may be destroyed by the obstacles. Particularly for those applications where the water is either shallow or filled with many obstacles, the prior art inboard and outboard motors are unsatisfactory.
To traverse the shallower bodies of water or those littered with obstacles, a generally flat bottom boat hull is preferred. In addition, the propeller drive shaft is extended beyond the boat by a much greater distance. When extended, the propeller can be driven shallowly in the water, free of interference with the boat. When an obstacle is encountered, the boat may pass over and be clear of the obstacle while still being propelled by the motor. Boats that use this type of drive system are sometimes referred to as mud boats, owing to their substantially improved propulsion in shallow waters, swamps, and other muddy waters. A number of U.S. patents are illustrative of the prior art, including U.S. Pat. No. 941,827 by Trouche, entitled “Motor more especially applicable for driving barges, wherries, flatboats, and the like”; U.S. Pat. No. 1,953,599 by Grimes, entitled “Boat propulsion device”; U.S. Pat. No. 2,096,223 by Chandler et al, entitled “Boat propelling mechanism”; U.S. Pat. No. 3,752,111 by Meynier, entitled “Pivoting motor boat drive unit”; U.S. Pat. No. 4,676,756 by Rodrigue et al, entitled “Boat and propulsion system including a transom platform”; U.S. Pat. No. 4,678,440 by Rodrigue et al, entitled “Boat and propulsion system”; the contents of each which are incorporated herein by reference.
On propulsion systems having an extended drive shaft, it is commonplace to use a housing or casing to surround the drive shaft. Frequently, some type of shroud or structure is also provided to prevent the propeller from directly striking any obstacles, and instead deflects the casing, drive shaft and propeller away from the obstacle. Additional features may be associated with the propeller and casing, such as various reinforcing elements, stiffeners or frameworks. The casing isolates the rotating propeller shaft from people and objects, thereby preventing the shaft from entangling or harming people or objects. The casing also protects the shaft from impact with hazards, and provides additional structural support to the drive shaft.
Some long shaft motors illustrated in the prior art anchor the motor on or within the boat, and provide a flexible coupling such as a universal joint somewhere along the long shaft, permitting the motor to stay in a fixed position and only requiring the propeller and some portion of the shaft to be manipulated for steering and propulsion. One exemplary patent, the teachings and contents which are incorporated herein by reference, is U.S. Pat. No. 3,430,603 by Parish, entitled “Sheering apparatus for a swamp boat.” Parish additionally illustrates another feature that is found in some mud motors, described therein as a cavitation plate. By placing the plate immediately above the prop, Parish observes that this plate reduces air-water turbulence at the prop, to increase the speed of the boat. U.S. Pat. No. 4,726,796 by Rivette J R et al, entitled “Driving and steering mechanism for boats,” the teachings and contents which are also incorporated herein by reference, describes an “antiventilation plate” immediately above and adjacent to the prop.
A number of additional patents exemplary of the broader marine art and most generally illustrating various plates or guides adjacent to a prop, the teachings and contents which are also incorporated herein by reference, include U.S. Pat. No. 682,027 by Burgess, entitled “Propulsion of vessels”; U.S. Pat. No. 904,313 by Davis, entitled “Hood for propeller wheels”; U.S. Pat. No. 2,442,728 by Kiekhaefer, entitled “Drive shaft housing for outboard motors”; U.S. Pat. No. 2,528,628 by Whitney, entitled “Ventilated underwater internal-combustion engine”; U.S. Pat. No. 2,549,477 by Kiekhaefer, entitled “Gear case unit for outboard motors”; U.S. Pat. No. 2,549,484 by Kiekhaefer, entitled “Underwater gear unit for outboard motors”; U.S. Pat. No. 2,656,812 by Kiekhaefer, entitled “Gear case unit for outboard motors”; U.S. Pat. No. 2,860,594 by Kiekhaefer, entitled “Splash deflector”; U.S. Pat. No. 2,896,565 by Stevens, entitled “Hydraulic flow control plate”; U.S. Pat. No. 3,151,597 by Larsen, entitled “Impact absorbing means for marine propulsion”; U.S. Pat. No. 3,587,510 by Shimanckas, entitled “Marine propulsion device with split drive shaft”; U.S. Pat. No. 3,599,595 by James, entitled “Outdrive for boats”; U.S. Pat. No. 3,768,432 by Spaulding, entitled “ ”; U.S. Pat. No. 4,295,835 by Mapes et al, entitled “High speed outboard drive unit”; U.S. Pat. No. 4,549,949 by Guinn, entitled “Marine propulsion device including cathodic protection”; U.S. Pat. No. 4,597,742 by Finkl, entitled “Trimming arrangement for planing hulls”; U.S. Pat. No. 4,636,175 by Frazzell et al, entitled “Water inlet for outboard propulsion unit”; U.S. Pat. No. 4,708,672 by Bentz et al, entitled “Boat stabilizer”; U.S. Pat. No. 4,744,779 by Koehler, entitled “Outboard motor cavitation plate extension”; U.S. Pat. No. 4,781,632 by Litjens et al, entitled “Anti-ventilation plate”; U.S. Pat. No. 4,804,312 by Schneekluth, entitled “Flow guide for ship propellers”; U.S. Pat. No. 5,207,605 by Kroeber, entitled “Outboard propeller guard”; U.S. Pat. No. 5,667,415 by Arneson, entitled “Marine outdrive with surface piercing propeller and stabilizing shroud”; U.S. Pat. No. 5,673,643 by Poppa, entitled “Hydrofoil accessory for marine propulsion device”; U.S. Pat. No. 5,800,224 by Ogino, entitled “Splash and anti-cavitation plate for marine drive”; U.S. Pat. No. 5,820,425 by Ogino et al, entitled “Outboard drive lower unit”; U.S. Pat. No. 6,155,893 by Belmont, entitled “Lift-generating device for a power boat”; U.S. Pat. No. 6,361,388 by Foreman, entitled “Marine motor drive assembly”; U.S. Pat. No. 6,482,057 by Schoell, entitled “Trimmable marine drive apparatus”; U.S. Pat. No. 6,966,806 by Bruestle et al, entitled “Replaceable leading edge for a marine drive unit”; U.S. Pat. No. 7,335,074 by Arneson, entitled “Shroud enclosed inverted surface piercing propeller outdrive”; U.S. Pat. No. 7,387,553 by Misorski et al, entitled “Marine drive unit overmolded with a polymer material”; and U.S. Pat. No. 7,575,490 by Angel et al, entitled “Passive air induction system for boats”. In addition to the foregoing patents, Webster's New Universal Unabridged Dictionary, Second Edition copyright 1983, is incorporated herein by reference in entirety for the definitions of words and terms used herein, unless explicitly otherwise defined herein.
An important issue for shallow water application is the location and inertia of the prop in the water. As aforementioned, there are many shallow obstacles. When an obstacle is encountered, the boat will typically strike the obstacle first. Desirably, the boat will be deflected, and, owing to the large area and significant framework typically found in a boat of this nature, the boat will be unharmed or sustain only cosmetic damage. The propeller will next encounter the hazard. The greater the mass at the end of a long shaft propeller, the more force that will be applied thereto to pivot the prop up and over the obstacle. Furthermore, the deeper the prop runs in the water, the more obstacles that will be encountered.
In the prior art, various plates nearby to the prop serve various purposes, depending upon design, but frequently are used as protection for the prop against direct impact with an obstacle such as a tree or rock. In addition, some artisans use a plate to “trim” the motor, setting the running angle of the prop in the water. As aforementioned, a few of these prior art plates were also described as anti-cavitation or anti-ventilation plates. Heretofore, with or without these various plates, the boat operator is required to manually control the depth of the prop, physically absorbing and damping the movements thereof while still trying to control the depth of the prop in the water most appropriately for each given instant. This proves to be both difficult and physically taxing.
Another limitation of the prior art has to do with the reliability and durability of these long shaft motors. In addition to the obstacles that can bend or destroy parts, the operation in shallow waters virtually ensures rapid wear and destruction of the seals that protect the bearings needed to support the rotating shaft. For the purposes of the present disclosure, it will be understood herein that bearings are used to refer to any type of member designed to permit one part to rotate with respect to another, and so will include oiled, greased or inherently lubricious parts such as are commonly referred to as bushings, ball or other types of roller or jeweled bearings, and any other known devices and apparatus that work accordingly. Unfortunately, as sand, dirt or other matter enters into the seals, the seals are rapidly destroyed. Once the seal is destroyed, the bearings are then exposed to excessive water flow and the very same matter that destroyed the seal. Consequently, once the seal fails, the life expectancy of the bearing is greatly reduced. Heretofore, commercially used seals and bearings have had a very short life expectancy, in some of the more extreme cases requiring replacement after only a few hours of operation in shallow, sandy-bottom waterways.